One approach adopted by motor vehicle manufacturers to reduce vehicle mass is to employ light metal castings. These castings are typically fabricated of aluminum or magnesium, with magnesium being favored due to its lower density.
Some of the commonly used magnesium-based alloys in automotive cast applications are identified as AM20, AM50, AM60, AZ31, AZ80, AZ91, AE42 and AE44. The designations A, M, Z, and E refer to major alloying elements in the magnesium alloy: aluminum (A), manganese (M), zinc (Z) and rare earth (E) and the numerical designations identify the nominal concentration of each element in weight percent. Hence all of these magnesium alloys contain aluminum as a significant alloying element in nominal proportion ranging from 2 to 9 weight percent.
But all of these alloys are prone to corrode in aqueous environments. Hence most of these cast magnesium alloys have been applied on components such as steering column components, instrument panel beams, clutch and brake pedal brackets, transmission cases and housings, among others, where no exposure to corrosive media is anticipated or any exposure may be well controlled. A broader range of applications may be anticipated if the corrosion performance of articles cast from such magnesium alloys may be improved.